Initial oxidation stages of hydrogen- and styrene-terminated Si(100) surfaces: A molecular dynamics study

We have studied the initial oxidation of H- and styrene-terminated Si(100)-2 × 1 films in O2 atmosphere at 500 K using molecular dynamics (MD) simulations based on a reactive force field. Our simulations show that for both surface terminations the primary reactions observed are the dissociation of the oxygen molecules and the simultaneous insertion of atomic oxygen in the SiSi back-bonds. On the H:Si(100)-2 × 1 surface, another reaction is the formation of isolated SiOH bonds via the insertion of an oxygen atom in a SiH bond. Detailed analysis of MD configurations shows that different vibrational modes of the surface SiH and the tilting of Si dimers at 500 K facilitate the breaking of the O2 molecule and the oxygen attack at backbonds. The combination of these reactions leads to increased amorphization of the surface as the oxidation proceeds. In the case of styrene-terminated Si(100)-2 × 1, the rate of O2 attack was much lower than on H-terminated surface and O-atom insertions were not observed in back-bonds of SiC bonds. In addition to lesser number of SiH sites on styrene-Si(100)-2 × 1, another significant reason for the lower rate of O2 attack was the repulsion of oxygen molecules resulting from the movement of phenyl rings in styrene at 500 K.